President Obama pulled the plug Friday on a long-delayed environmental regulation that would have further limited industrial smog emissions, leaving in place an ozone standard that EPA administrator Lisa Jackson recently described as "legally indefensible."

The proposed limits have been under assault by congressional Republicans and the business community for months. House Majority Leader Eric Cantor (R-VA) recently called it "possibly the most harmful of all the currently anticipated Obama Administration regulations."

Obama's decision comes the same day new employment figures show the economy created zero net jobs in August.

What was the regulation, and what does it mean now that it's been scotched? In short, it means Bush-era smog standards, declared inadequate by government science advisers, will likely remain in effect until mid-decade if not longer.

EPA warns that breathing ground-level ozone (smog) "can trigger a variety of health problems including chest pain, coughing, throat irritation, and congestion. It can worsen bronchitis, emphysema, and asthma. Ground-level ozone also can reduce lung function and inflame the linings of the lungs. Repeated exposure may permanently scar lung tissue."

In 2006, EPA's scientific advisers recommended the agency limit ground-level ozone to an ambient concentration of 60-70 parts per billion. The Bush administration responded in typical fashion by setting the standard at 75 ppb, in apparent violation of the Clean Air Act.

When President Obama came to power, and Jackson was confirmed to head EPA, the agency began the process of reviewing and strengthening the regulation. After multiple delays, based largely on industry concerns about cost, Obama pulled the plug. In his statement announcing the decision, Obama noted that "[w]ork is already underway to update a 2006 review of the science that will result in the reconsideration of the ozone standard in 2013. Ultimately, I did not support asking state and local governments to begin implementing a new standard that will soon be reconsidered."

But in a conference call with reporters, two White House officials acknowledged, implicitly, that it could take months or years beyond the publication of the new standard in 2013. Asked by a reporter how quickly a new regulation could be written after the 2013 standards, one official offered no specifics but said it would have to go through "the normal notice and comment process," which often takes over a year." And that's if Obama is re-elected.

A Republican administration could continue to flout the requirements of the Clean Air Act, while challenges dragged on in the courts for years.

The officials on the White House call front-loaded their statements with a list of largely unrelated administration environmental accomplishment — plainly sensitive to the magnitude of the decision, and to the degree that it will count as a blemish on Obama's environmental record.

The Chamber of Commerce reacted to the decision with unrestrained glee. "This an enormous victory for America's job creators, the right decision by the President, and one that will help reduce the uncertainty facing businesses. It's also a big first step in what needs to be a broader regulatory reform effort," it said in a statement. The House Republican leadership also hailed the decision.

Meanwhile, environmental groups were unrestrained in their disdain toward the decision. "The Obama administration is caving to big polluters at the expense of protecting the air we breathe," League of Conservation Voters President Gene Karpinski said in a statement. "This is a huge win for corporate polluters and huge loss for public health."

One administration official told reporters that the decision was made on the merits, but did acknowledge tellingly that "the President has directed me and all of us under Executive Order 13564 to be careful about regulations that impose significant cost on the private sector."